Hermetically sealed compression bonded circuit assembly having a suspension for compression bonded semiconductor elements

ABSTRACT

A harmetically sealed circuit assembly (10) containing a plurality of circuit elements (74, 76 and 80) which are to be compression bonded upon application of a force through opposed first and second walls (12, 20) of a hermetically sealed chamber containing the circuit elements to be compression bonded in accordance with the invention includes a plurality of columns (20-30) within the chamber with each circuit element to be compression bonded being disposed in a separate column; an inelastically deformed element (124-132) positioned in each of the columns outside the chamber having a first surface facing an outside surface of one of the first and second walls of the hermetically sealed chamber and a second surface with each of the second surfaces of the deformed springs facing an outside surface of another of the first and second walls; and a thickness of the columns measured between the outside surfaces of the first and second walls prior to compression bonding being substantially identical.

DESCRIPTION

1. Cross-Reference To Related Applications

Reference is made to the following related applications which are filedon even date herewith and which are incorporated herein by reference intheir entirety.

(1) Method of Manufacturing Hermetically Sealed Compression BondedCircuit Assemblies, U.S. Ser. No. 07/351,537.

(2) Compression Bonded Semiconductor Device Having a Plurality ofStacked Hermetically Sealed Circuit Assemblies, U.S. Ser. No.07/226,683.

(3) Hermetically Sealed Compression Bonded Circuit Assembly HavingFlexible Walls at Points of Application of Pressure for CompressionBonding Circuit Elements, U.S. Ser. No. 07/226,741.

2. Technical Field

The present invention relates to an individual hermetically sealedcircuit assembly having a plurality of circuit elements to becompression bonded which are contained in a hermetically sealed chamber,to one or more stacked hermetically sealed circuit assemblies which haveforce applied to compression bond the circuit elements within the one ormore circuit assemblies and to a process for manufacturing hermeticallysealed circuit assemblies. The present invention also relates to circuitassemblies of the foregoing type which are useful for high powerapplications such as in inverters in airframes for converting DC to AChaving reduced weight, high reliability, faster switching speeds andhigher efficiency.

3. Background Art

Compressive bonded semiconductor elements are widely in use. Thesesemiconductor elements establish electrical and thermal contact withoutexternal leads by means of a force applied orthogonal to surfaces of thesemiconductor elements to be compression bonded. Manufacturers ofcompression bonded semiconductor elements specify a nominal desiredcompressive bonding pressure at which the semiconductor elements are tooperate plus a range around the nominal pressure at which each elementis designed to operate. The specified pressure varies depending upon thetype of the element and its design. Operation outside the specifiedpressure range can cause circuit malfunction or failure of thecompression bonded elements.

Hermetically sealed circuit assemblies having two or more compressionbonded circuit elements contained within a hermetically sealed chamberare known. U.S. Pat. No. 3,575,574 discloses individual non-hermeticallysealed circuits each containing three compression bonded elements whichare contained in a stack having a plurality of the circuit assemblies.The stack is contained in a hermetically sealed chamber. Supports forthe individual circuit assemblies do not include any structures forequalizing force between the different columns of compression bondedcircuit elements of the stack of circuit assemblies. Furthermore,stacked individual circuit assemblies each having three circuit elementsto be compression bonded which are disposed in three columns do notpresent as serious a problem in achieving specified operating pressuresas circuit assemblies having four or more circuit elements to becompression bonded. A universal joint is disclosed in the '574 patentwhich provides for adjustable movement of heat sinks with respect to thecompression bonded circuit element. U.S. Pat. No. 4,313,128 discloses asingle hermetically sealed power hybrid circuit assembly. A heat sink tocontrol operating temperature thermally contacts the compression bondedpower circuit elements which extends below the bottom wall of ahermetically sealed chamber containing the compression bonded circuitelements. The hermetically sealed semiconductor circuit assemblydisclosed in the '128 patent is not designed to be stacked in a stackincluding multiple circuit assemblies which are clamped together toprovide the requisite compressive force for operation. The conpressiveforce in the device disclosed in the '128 patent is established by thebonding of the top and bottom walls of the hermetically sealed chamberthrough a side member.

Single compression bonded circuit elements in a hermetically sealedchamber are commercially available. These hermetically sealed circuitelements may be stacked and compression bonded by clamping the stack.These elements may have a corrugation in the opposed surfaces definingthe hermetically sealed chamber which provides for relieving stressesdue to welding and brazing.

Corrugated bus structures are known to relieve stress. U.S. Pat. No.4,583,005 discloses a circular corrugated bus and a spider-likeconductor which each contain corrugations for relieving thermal stress.A plurality of rings of semiconductor devices are electrically contactedwith the circular bus. The individual semiconductor devices are alsocontacted by the spider-like conductor.

Clamping structures for compressively loading stacked compression bondedsemiconductor circuit elements which apply force to a central axiscontaining the stacked semiconductor circuit elements are known. U.S.Pat. No. 4,504,850 discloses the clamping of a stack of compressionbonded circuit elements by application of a force to a convex surface atthe axis of the stacked semiconductor circuit elements. Furthermore,swivel, ball and gimbal mounts are known for performing the function ofthe convex surface to apply uniform force to the central axis of thestacked semiconductor element.

Mechanisms for applying force to columns of stacked compression bondedcircuit elements are known. These mechanisms use a force applying memberto apply a force to the central axis of the stacked compression bondedsemiconductor elements which is sufficient to apply the requisitepressure for normal operation. Bellville washers have been used to applyforce to each column of stacked semiconductor circuit elements. See U.S.Pat. No. 3,551,758. Furthermore, coil springs have been used to apply anaxial force to each of the columns of stacked semiconductor compressionbonded devices by application to an end part of the stack. See U.S. Pat.No. 3,573,574 discussed above. Additionally, it is known to applycompressive force to load stacked compression bonded semiconductorcircuit elements by the application of torque to a threaded connectingmember which is attached to rigid end plates of the stack. See U.S. Pat.Nos 3,652,903, 3,936,704 and 4,268,850.

Individual compressed coil springs have been used to load pairs ofsemiconductor elements to establish desired operating pressure. Opposedfaces of the coil spring are in surface contact with first and secondcompression bonded semiconductor devices. See U.S. Pat. No. 3,921,201.

Compression bonding of a plurality of individual circuit assemblies eachhaving four or more semiconductor elements contained in four or morecolumns presents special problems in achieving the desired operatingpressures in each of the columns. This problem is analogous to levelinga four legged chair in which any variation in the length of one of thelegs will cause three of the legs to lie in a single plane with thefourth leg not being in surface contact with the plane containing thethree legs unless each of the legs is exactly of the same length. It isfor this reason that the establishment of desired operating pressuresfor compression bonded circuit assemblies are more easily establishedwhen only three compression bonded circuit elements disposed in separatecolumns to be compression bonded are contained in each circuit assemblyof a stack of multiple circuit assemblies.

DISCLOSURE OF INVENTION

The present invention is a method of manufacturing a semiconductordevice having at least one hermetically sealed compression bondedcircuit assembly disposed in a stack to which a force is applied tocolumns containing at least one compression bond circuit element withinthe stack of individual circuit assemblies. The invention also is ahermetically sealed circuit assembly, containing at least one circuitelement to be compression bonded, with each circuit element beingsuspended in separate columns by deformed shims, springs or adistributed spring function within the columns within or outside thehermetically sealed circuit assembly with each circuit element beingcompression bonded upon the application of a force to opposed first andsecond walls of a hermetically sealed chamber containing the circuitelements. Moreover, the invention is a hermetically sealed circuitassembly containing at least one circuit element to be compressionbonded with each circuit element being disposed in a separate columnwith the at least one circuit element being compression bonded by theapplication of force to first and second walls of a hermetically sealedchamber containing the circuit elements with the walls and circuit buseswithin the chamber containing structures which permit flexation of thecolumns of the at least one circuit elements within the hermeticallysealed circuit assembly. Finally, the invention is a compression bondedsemiconductor device having at least one individual hermetically sealedcircuit assembly contained in a stack to which is applied a force tocompression bond at least one individual circuit element within theindividual hermetically sealed circuit assemblies with the at least oneindividual circuit element of each circuit assembly being located inaligned columns within the stack.

With the invention individual hermetically sealed circuit assemblieshaving any number of compression bonded circuit elements may be madewhile maintaining pressure on the individual circuit elements within arange of operation pressure provided for the individual circuitelements. The individual circuit elements of each hermetically sealedcircuit assembly are suspended in columns in the stack of hermeticallysealed compression bonded circuit assemblies by individual deformablespacers which are located in the individual columns containing thecompression bonded circuit elements between each of the circuitassemblies. The deformed spacers, which may be springs or shimsdepending upon the application conditions regarding generated heat, havefirst and second opposed surfaces with the first surface of each of thespacers facing an outside surface of a wall of a hermetically sealedchamber of the circuit assembly and a second surface which is located ina plane parallel to the opposed parallel walls of the chamber. Thisrelationship insures that the individual circuit assemblies within thestack have uniform thickness at each of the points of contact within thecolumns of compression bonded circuit elements within the stack withadjacent circuit assemblies that produces uniform pressure on each ofthe compression bonded circuit elements within the column in the stackupon clamping to maintain the compression bonded circuit elements withinthe pressure specification of operation for the circuit elements.Furthermore, if the inelastically deformed spacers are chosen to besprings, the springs are chosen to have a spring rate which, duringthermal cycling of operation of the circuit element, maintains pressureon the compression bonded circuit elements within the range of pressurespecified for operation of the compression bonded circuit elements.

The preferred method of deforming the deformable spacers is to positionthe individual compression bonded circuit assembly on a flat surfacewith the spacers disposed outside and facing a wall of a hermeticallysealed chamber containing the one or more individual circuit elements tobe compression bonded and compressing the individual spacers past theiryield point with a surface which is parallel to the surface on which thecircuit assembly is resting to cause the surface of the spacers to liewithin a plane which is parallel to the walls of the chamber of thehermetically sealed circuit assembly to eliminate any substantialvariation in thickness of the columns measured between the deformedspacer within the column and one of the walls of the chamber oppositethe wall facing the deformed spacer.

The opposed walls of the chamber of the hermetically sealed circuitassembly are provided with opposed pairs of annular corrugationsdefining columns within which circuit elements to be compression bondedare positioned that permit each of the individual circuit elements to becompression bonded to move in any direction without applying torsionalor other loads to any other of the compression bonded circuit elementswhich would vary the pressure applied to the any other of thecompression bonded circuit elements at least to an extent to varypressure applied to the any other compression bonded circuit elementsoutside a desired range of pressure operation of the compression bondedcircuit elements. This configuration permits each of the compressionbonded circuit elements to "float" within the columns of the circuitassembly which insures that each of the compression bonded circuitelements may be maintained within its specified pressure range ofoperation. Furthermore, each of the circuit buses located within theindividual hermetically sealed circuit assemblies contains at least onecorrugation located between connections between the outside of thehermetically sealed circuit and an adjacent compression bonded circuitelement which is in electrical contact with the circuit bus and at leastone corrugation located between any compression bonded circuit elementswhich are in electrical connection with the circuit bus. Thecorrugations of the circuit buses which connect individual compressionbonded circuit elements and which further connect compression bondedcircuit elements with circuit connections to the exterior of thehermetically sealed chamber prevent substantial torsional or other loadsfrom being applied from one of the compression bonded circuit elementsin one column to another of the compression bonded circuit elements inanother column which would significantly vary the pressure applied tothe adjacent compression bonded circuit elements at least to an extentto vary pressure applied to the any other compression bonded circuitelement outside a desired range of pressure operation. Thesecorrugations further enhance the "floating" of the individualcompression bonded circuit elements within the column to maintainoperating pressure within the range of operating pressure specified forthe individual compression bonded circuit elements.

If individual deformed spacers, which are located within the columns ofstacked compression bonded circuit elements within the stack ofindividually hermetically sealed circuit assemblies are chosen to besprings because of thermal expansion during operation in the applicationof the circuit, each spring is chosen to have a spring rate as afunction of a specified operating pressure of the compression bondedcircuit element which is located in the column containing the spring.The spring rate of each spring is chosen to maintain a pressure on thecompression bonded circuit element that the spring is in axial alignmentto be within the specified operating range of pressure of the circuitelement during operation induced thermal cycling of the hermeticallysealed circuit assembly.

Preferably, a heat exchanger is connected to and in thermal contact withan outside surface of a wall of the chamber of the hermetically sealedcircuit to control thermal cycling of the individual compression bondedcircuit elements within the chamber. The heat exchanger has first andsecond surfaces which are parallel to the first and second walls of thechamber. Preferably, the aforementioned spacers are deformed with theheat exchanger in contact with the wall of the chamber to insure thatthe plane containing the surfaces of the deformed spacers is parallel tothe outside surfaces of the heat exchanger and the walls of the chamber.The heat exchanger may optionally be provided with passages for acooling fluid to further control the temperature range of thecompression bonded circuit elements during operation. If the heatexchanger effectively controls the cycling of operating temperature ofthe individual compression bonded circuit elements during operation,deformed shims may be used in place of the deformed springs for thereason that thermal expansion will be minimized to eliminate thenecessity of compensating for thermal expansion of the individualcompression bonded circuit elements within the columns of the stack ofcompression bonded circuit elements which could cause variation inoperating pressure outside the specified pressure range for operation.

The spring in each column may alternatively be implemented by beingdistributed in one or more additional elements within each column of ahermetically sealed circuit assembly either within and/or outside ahermetically sealed chamber containing the circuit elements to becompression bonded. For example, both a deformed spacer and the heatexchanger may contribute part of the spring function. Furthermore, oneor more additional elements within the chamber may contribute part of orall of the spring function.

When a plurality of circuit assemblies are stacked together, it is notnecessary that each individual circuit assembly be identical.Furthermore, while an identical number of columns should be present inthe stack of circuit assemblies to insure loading of the individualcompression bonded circuit elements within the columns, a spacer, whichdoes not perform a circuit function, may be located in one or morecolumns within the hermetically sealed chamber having a thicknesssimilar to the thickness of the columns inside the chamber havingcompression bonded circuit elements to permit individual circuitassemblies having different numbers of compression bonded circuitelements to be placed in the stack.

A hermetically sealed circuit containing a plurality of circuit elementswhich are to be compression bonded upon application of a force throughopposed first and second walls of a hermetically sealed chambercontaining the circuit elements to be compression bonded in accordancewith the invention includes a plurality of columns within the chamberwith each circuit element to be compression bonded being disposed in aseparate column; an elastically spring positioned in each of the columnsoutside the chamber having a first surface facing an outside surface ofone of the first and second walls of the hermetically sealed chamber anda second surface with each of the second surfaces of the deformedsprings facing an outside surface of another of the first and secondwalls; and a thickness of the columns measured between the outsidesurfaces of the first and second walls prior to compression bondingbeing substantially identical. Each deformed spring has a spring ratewithin a range which is a function of the circuit element in the columnwhich contains the deformed spring. Each of the second surfaces of thedeformed springs being disposed in a single plane. The spring maycomprise at least one ring with each ring being concentric with an axisof the column within which the ring is contained and having a C-shapedcross section in which opposite ends of the C are inelastically deformedtoward each other or, alternatively, a lattice having open cellsdefining columns intersecting the first and second walls. A plurality ofcircular corrugations are provided within the first wall of the chamberin a spatial configuration with each corrugation determining a spatiallocation within the circuit assembly of a circuit element to becompression bonded and a plurality of circular corrugations are providedwithin the second wall of the chamber in a spatial configurationidentical to the spatial configuration of the corrugations in the firstwall, each corrugation of the second wall respectively being opposed toa corrugation in the first wall with pairs of opposed corrugations inthe first and second walls defining a column; and a different deformedspring being positioned outside the chamber within each differentcorrugation within the second wall. At least one circuit bus is providedhaving first and second opposed surfaces which are substantiallyparallel to each other and to the first and second walls of thehermetically sealed circuit assembly, the at least one circuit bushaving at least one corrugation therein. The circuit assembly has anopening through which at least one circuit connection extends, at leastone corrugation being within each at least one circuit bus between thecircuit connection and a point of electrical contact with a circuitelement to be compression bonded and at least one corrugation beingwithin each of the at least one circuit buses between any circuitelements to be compression bonded which are in electrical contact withone of the at least one circuit buses. A control circuit is disposedinside the chamber having circuit control elements for controlling theplurality of circuit elements to be compression bonded within thechamber and the control circuit has a plurality of contacts which areeach respectively connected to a different circuit bus. At least twocircuit buses may be contained in the chamber and portions of onecircuit bus overlie another circuit bus within the chamber. A heat sinkis provided having first and second parallel surfaces with the firstsurface of the heat sink being in surface and thermal contact with anoutside surface of the first wall. The plurality of circularcorrugations within the first wall each form a recess which projectsoutward from the chamber. The plurality of circular corrugations withinthe second wall each form a recess which projects inward toward thechamber. Each of the deformed springs is positioned within a differentone of the recesses within the second wall and the single plane isspaced from the second wall of the chamber to an exterior side of thechamber.

A hermetically sealed circuit assembly containing a plurality of circuitelements which are to be compression bonded upon application of a forcethrough opposed first and second walls of a hermetically sealed chambercontaining the circuit elements to be compression bonded in accordancewith the invention includes a plurality of columns within the chamberwith each circuit element to be compression bonded being disposed in aseparate column; an inelastically deformed shim positioned in each ofthe columns outside the chamber having a first surface facing an outsidesurface of one of the first and second walls of the hermetically sealedchamber and a second surface with each of the second surfaces of thedeformed shims facing an outside surface of another of the first andsecond walls and a thickness of the columns measured between the outsidesurfaces of the first and second walls prior to compression bondingbeing substantially identical. Each of the second surfaces of thedeformed shims being disposed in a single plane. The shim may comprise amolded resin in accordance with AMS 3726-1-2-3. A plurality of circularcorrugations are provided within the first wall of the chamber in aspatial configuration with each corrugation determining a spatiallocation within the circuit assembly of a circuit element to becompression bonded and a plurality of circular corrugations are providedwithin the second wall of the chamber in a spatial configurationidentical to the spatial configuration of the corrugations in the firstwall, each corrugation of the second wall respectively being opposed toa corrugation in the first wall with pairs of opposed corrugations inthe first and second walls defining a column; and a different deformedshim being positioned outside the chamber within each differentcorrugation within the second wall. At least one circuit bus is providedhaving first and second opposed surfaces which are substantiallyparallel to each other and to the first and second walls of thehermetically sealed circuit assembly, the at least one circuit bushaving at least one corrugation therein. The circuit assembly has anopening through which at least one circuit connection extends, at leastone corrugation being within each at least one circuit bus between thecircuit connection and a point of electrical contact with a circuitelement to be compression bonded and at least one corrugation beingwithin each of the at least one circuit buses between any circuitelements to be compression bonded which are in electrical contact withone of the at least one circuit buses. A control circuit is disposedinside the chamber having circuit control elements for controlling theplurality of circuit elements to be compression bonded within thechamber and the control circuit has a plurality of contacts which areeach respectively connected to a different bus. At least two circuitbuses may be contained in the chamber and portions of one circuit busoverlie another circuit bus within the chamber. A heat sink is providedhaving first and second parallel surfaces with the first surface of theheat sink being in surface and thermal contact with an outside surfaceof the first wall. The plurality of circular corrugations within thefirst wall each form a recess which projects outward from the chamber.The plurality of circular corrugations within the second wall each forma recess which projects inward toward the chamber. Each of the deformedshims is positioned within a different one of the recesses within thesecond wall and the single plane is spaced from the second wall of thechamber to an exterior of the chamber.

A hermetically sealed circuit assembly containing a plurality of circuitelements which are to be compression bonded upon application of aclamping force through opposed first and second walls of a hermeticallysealed chamber containing the circuit elements to be compression bondedin accordance with the invention includes a plurality of columns withinthe chamber with each circuit element to be compression bonded beingdisposed in a separate column; an inelastically deformed spacerpositioned in each of the columns outside chamber having a first surfacefacing an outside surface of one of the first and second walls of thehermetically sealed chamber and a second surface with each of the secondsurfaces of the deformed spacers facing an outside surface of another ofthe first and second walls; a thickness of the columns measured betweenthe outside surfaces of the first and second walls prior to compressionbonding being substantially identical. Each of the second surfaces ofthe deformed shims being disposed in a single phase. A plurality ofcircular corrugations are provided within the first wall of the chamberin a spatial configuration with each corrugation determining a spatiallocation within the circuit assembly of a circuit element to becompression bonded and a plurality of circular corrugations are providedwithin the second wall of the chamber in a spatial configurationidentical to the spatial configuration of the corrugations in the firstwall, each corrugation of the second wall respectively being opposed toa corrugation in the first wall with pairs of opposed corrugations inthe first and second walls defining a column and a different deformedspacer being positioned outside the chamber within each differentcorrugation within the second wall. At least one circuit bus is providedhaving first and second opposed surfaces which are substantiallyparallel to each other and to the first and second walls of thehermetically sealed circuit assembly, the at least one circuit bushaving at least one corrugation therein. The circuit assembly has anopening through which at least one circuit connection extends, at leastone corrugation being within each at least one circuit bus between thecircuit connection and a point of electrical contact with a circuitelement to be compression bonded and at least one corrugation beingwithin each of the at least one circuit buses between any circuitelements to be compression bonded which are in electrical contact withone of the at least one circuit buses. A control circuit is disposedinside the chamber having circuit control elements for controlling theplurality of circuit elements to be compression bonded within thechamber and the control circuit has a plurality of contacts which areeach respectively connected to a different bus. At least two circuitbuses may be contained in the chamber and portions of one circuit busoverlie another circuit bus within the chamber. A heat sink is providedhaving first and second parallel surfaces with the first surface of theheat sink being in surface and thermal contact with an outside surfaceof the first wall. The plurality of circular corrugations within thefirst wall each form a recess which projects outward from the chamber.The plurality of circular corrugations within the second wall each forma recess which projects inward toward the chamber. Each of the deformedspacers is positioned within a different one of the recesses within thesecond wall and the single plane is spaced from the second wall of thechamber to an exterior side of the chamber.

A hermetically sealed circuit assembly containing a plurality of circuitelements which are to be compression bonded upon application of a forcethrough opposed first and second walls of a hermetically sealed chambercontaining the circuit elements to be compression bonded in accordancewith the invention includes a plurality of columns disposed within thechamber each containing a separate element to be compression bonded; aninelastically deformed spacer positioned in each of the columns outsidethe chamber having a first surface facing an outside surface of one ofthe first and second walls of the hermetically sealed chamber and asecond surface with each of the second surfaces of the deformed spacersfacing an outside surface of another of the first second walls; athickness of the columns measured between the outside surfaces of thefirst and second walls prior to compression bonding being substantiallyidentical; and a distributed spring function contained in at least oneelement within each column. Each distributed spring function has aspring rate within a range which is a function of the circuit element tobe compression bonded in the column which contains the distributedspring function. The at least one element may be one or more of at leastthe deformed spacer and a heat sink in surface contact with one of thefirst and second walls.

As used herein the terminology "parallel" or "substantially parallel" indescribing the relationship of opposed surfaces of deformed shims,deformed springs and deformed spacers means a spatial relationship ofopposed surfaces which is achieved by moving of two parallel surfacestoward each other to load the shims, springs or deformable spacers, witha load causing inelastic deformation of the shims, springs or spacers ina direction parallel to the applied force.

Furthermore, the terminology "parallel" or "substantially parallel" indescribing the relationship of opposed surfaces of a heat sink or wallsof a chamber means the surfaces are as close to being perfectly parallelas necessary to achieve operation of compression bonded circuit elementswithin circuit assemblies in accordance with a range of pressures atwhich the circuit elements are specified to operate.

As used herein the terminology "deformed" in describing a shim, spaceror spring means a shim, spacer or spring to which has been applied aforce which inelastically reduced a dimension of the shim, spacer orspring parallel in the direction of the applied force which force isgreater in magnitude than a force applied to compression bond circuitelements in circuit assemblies containing the shim, spacer or spring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 illustrate an exploded view of an individual hermeticallysealed circuit assembly in accordance with the invention.

FIG. 4 is a circuit schematic of the circuit illustrated in FIG. 2.

FIG. 5 is a perspective view of a deformable shim in accordance with theinvention.

FIG. 6 is a cross-sectional view of a first form of deformable spring inaccordance with the present invention.

FIG. 7 is a perspective view of a second form of deformable spring inaccordance with the present invention.

FIG. 8 is a top plan view of a hermetically sealed compression bondedcircuit assembly in accordance with the present invention.

FIG. 9 is a sectional view of FIG. 8 along section line 9--9.

FIG. 10 is a sectional view of FIG. 8 along section line 10--10.

FIG. 11 is a sectional view of FIG. 8 along section line 11--11.

FIG. 12 is a sectional view of FIG. 8 along section line 12--12.

FIG. 13 illustrates the process for deforming the deformable spacers ofthe present invention.

FIG. 14 illustrates a compression bonded stack of circuits in accordancewith the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1-3 illustrate an exploded view of a single hermetically sealedhybrid circuit assembly 10 in accordance with the invention. Likereference numerals identify like parts in FIGS. 1-14. As will bedescribed below with reference to FIG. 14, the preferred application ofthe individual hermetically sealed hybrid circuit assembly 10 of FIGS.1-3 is in a stack containing at least one circuit assembly with eachcircuit assembly having a plurality of circuit elements to becompression bonded. The circuit elements to be compression bonded areindividually located in separate columns within the stack. A clampapplies force to the stack to apply pressure within a specified range ofoperation of each of the circuit elements to be compression bondedcontained in each of the circuit assemblies. It should be understoodthat the columns discussed below with reference to the individualcircuit assemblies 10 are in identical axial locations as the axiallocations of the columns discussed with reference to the stack ofindividual circuit assemblies in FIG. 14. Metallic pan 12 has a flatsection 14 and a closed wall 16 which projects upward from the flatsection. The wall 16 contains a lip 18 which is joined by a process suchas cold welding to a lid 20 to form a hermetically sealed chamberdisposed between the flat section 14 and the lid 20. A plurality ofcolumns 22-30 are contained in each circuit assembly in which circuitelements to be compression bonded are located as described below. Theflat section 14 contains circular corrugations 32-40 which arerespectively concentric to the axis of the columns 22-30 and whichproject outward into the chamber. It should be understood that each ofthe corrugations 32-40 may be comprised of one or more concentricannular rings which are formed in the metal of the flat section 14 byconventional processing such as stamping. The corrugations 32-40 areprovided in the flat section 14 to permit freedom of movement of theportion of the flat section 14 at least within the columns 22-30 in anydirection without transmitting substantial torque or loads(cantilevered) from one of the compression bonded circuit elements toany other of the compression bonded circuit elements which substantiallyaffects pressure applied to the any other compression bonded circuitelements at least to an extent to vary pressure applied to the any othercompression bonded circuit elements outside a desired pressure range ofoperation. Preventing transmission of substantial torque or loads is animportant part of the present invention maintaining pressure onindividual circuit elements within the range of pressure for operationspecified for the individual circuit elements to be compression bonded.The corrugations 32-40 are further useful for defining the location ofthe columns 22-30 to permit the components within each of the columns tobe easily located therein. A pair of identical circuit connections 42connect the pan 12 to external circuits (not illustrated). Asillustrated, the circuit connections 42 are connected to the collectorsof transistors to be compression bonded which are contained within thehermetically sealed chamber defined by the flat section 14, wall 16 andthe lid 20. Bus connections 44, 46 and 48 respectively connect the diodebus 50, diode bus 52 and emitter bus 54 with the exterior of the chamberdefined by the flat section 14, wall 16 and lid 20.

Each of the circuit buses 50, 52, and 54 contains at least onecorrugation which is disposed between a point of electrical contact witha circuit bus connector and a point of electrical contact with a circuitelement to be compression bonded and one or more additional corrugationsas, for example 64, in each circuit bus disposed between any circuitelements to be compression bonded which are in electrical contact withthe circuit bus. The corrugations permit the circuit bus to freely flexin between rigid points of contact which are with the circuit busconnections 44-48 and with the individual circuit elements to becompression bonded and with any circuit elements to be compressionbonded which are connected by a circuit bus. The corrugations preventthe application of torque or loading between the circuit bus connectionsand circuit elements to be compression bonded or between circuitelements to be compression bonded which are electrically connected tothe circuit bus at least to an extent that varies pressure applied tothe compression bonded circuit elements outside a desired pressure rangeof operation. Specifically, the diode bus 50 contains corrugations 56and 58; the diode bus 52 contains corrugation 60; emitter bus 54contains corrugations 62, 64 and 66 and Darlington bus 68 containscorrugations 70 and 72. To the base contacts 69 for transistors 76.

It should be understood that the present invention is not limited to theparticular circuit configuration illustrated in FIGS. 1-4 with thecircuit elements to be compression bonded in the chamber defined by theflat section 14, wall 16 and lid 20 being described as follows. Abipolar driver transistor 74 is an input to a pair of matched bipolardriven transistors 76 which are connected to the driver transistor in aconventional Darlington configuration. Furthermore, diodes 78 and 80 arecircuit elements to be compression bonded. A control circuit 82, whichmay be any conventional integrated circuit or other circuit which is notto be compression bonded, is provided in an area of the flat section 14where compressive force is not applied. The control circuit may performthe function of a Baker clamp. It should be understood that the controlcircuit 82 may perform any control function which is desired to beutilized with the circuit elements to be compression bonded. Electricalconnections between the control contacts 84 and the exterior of thecircuit have been omitted for purposes of clarity. Similarly, electricalconnections in the interior of the chamber between the output of thecontrol circuit 82 and the various compression bonded circuit elementshave been omitted. The omitted electrical connections may be determinedfrom FIG. 4. For example, base contact 86, which is electricallyconnected to the base of the driver transistor 74, is connected to thecontrol circuit 82 by a flex circuit (not illustrated) spanning thedisplacement between contact point 88 and the control circuit. Each ofthe collectors of bipolar transistors 74-76 are respectivelyelectrically connected to an interior surface of the flat section 14within the circular area defined by circular corrugations 32, 36 and 38by means of a soft metal foil 90. The soft metal foil 90 insures thatupon application of the compressive force by a clamp to a stack ofhermetically sealed circuit assemblies 10 that there will be completethermal and electrical contact between the collectors of the bipolartransistors 74-76, the flat section 14, and the circuit connections 42,and thermal conduction from the circuit assembly if a heat sink isconnected to an outside surface of the flat section 14 as describedbelow with reference to FIG. 13. Soft metal disk 92 provides fullelectrical and thermal contact between the diode 78 and diode bus 50.Soft metal foil disk 94 provides complete electrical contact between thediode 78 and the end portion 96 of emitter bus 54. Soft metal foil disk98 provides complete and thermal electrical contact between diode 80 andspacer 100. Soft metal foil disk 102 provides thermal and electricalcontact with the annular recess defined by circular corrugation 40. Apair of annular insulative spacers 104 are provided. A ceramic diskspacer 105 providing electrical insulation and thermal conductivity isdisposed between diode bus 50 and the flat section 14 in the annularrecess defined by circular corrugation 34. The bushing 105 may bemetallized to improve thermal contact.

Furthermore, it should be understood that the invention is not limitedto having a compression bonded circuit element disposed in each of thecolumns 22-30. An insulative spacer 107 may be disposed in one or moreof the columns within the hermetically sealed chamber of a circuitassembly which are not performing a circuit function to permitindividual circuit assemblies 10 having differing numbers of compressionbonded circuit elements to be compression bonded in a single stack. Forexample, the insulative spacer 107 having a thickness similar to thecombined thickness of the elements in columns 24-30 within thehermetically sealed chamber could be inserted in the column 22 toprovide a conventional Darlington amplifier with only a single outputstage.

FIG. 2 illustrates an exploded view comprised of the circuit assembly 10consisting of the components discussed above with reference to FIG. 1,insulating sheet 106, and the lid 20. The insulating sheet 106 isprovided to electrically isolate the exposed top portions of the diodebus 50, diode bus 52, emitter bus 54 and the Darlington bus 68 from thelid 20. As illustrated, the diode bus 50 is disposed beneath the endportion 96 of the emitter bus 54; the Darlington bus base contacts 69 isdisposed below intermediate portions 108 and 110 of the emitter bus 54.Furthermore, insulator 112 electrically isolates the bottom surface ofthe emitter bus 54 from base contacts 69 of the Darlington bus 68.Circular corrugations 114-122 are provided in the lid 20 which arerespectively concentric with columns 22-30 so that the corrugationsrespectively are disposed above and axially aligned in opposed pairswith the corrugations 32-40. Each of the circular corrugations 114-122forms a recess which projects inward toward the hermetically sealedchamber which is formed by joining the closed wall 16 of pan 12 to thelid 20. Opposed pairs of the corrugations 32- 40 and 114-122 are eachdisposed in a separate column 22-30. The corrugations 114-122 performtwo functions which are to axially locate the deformable spacers124-132, discussed below with reference to FIG. 3, and to permit theportion of the lid 20 within the columns 22-30 to flex in any directionwithout transmitting substantial torque or loads (cantilevered) from oneof the circuit elements to be compression bonded to another of thecircuit elements to be compression bonded which substantially affectspressure applied to any other compression bonded circuit elements atleast to an extent that varies pressure applied to the compressionbonded circuit elements outside a desired pressure range of operation.It should be understood that each of the corrugations 114-122 may becomprised of one or more concentric annular rings which are formed inthe metal of the lid 20 by conventional processing such as stamping. Theannular recess formed by each of the circular corrugations 114-122receives a deformable spacer which may be a spring or shim as discussedbelow with reference to FIGS. 3 and 13. The lip 18 is joined to the lid20 by a process such as cold welding or brazing to form a hermetic sealdefining the chamber having opposed parallel walls which respectivelyare the flat section 14 and the lid 20.

FIG. 3 illustrates an exploded view of the assembled components of FIG.2 and deformable spacers 124-132 and load washers 144-152 which arecontained in the columns 22-30. Load washers 144-152 and deformablespacers 124-132 are held in place by insulator sheet 153 which is bondedto lid 20 of assembly 10. The deformable spacers 124-132 arerespectively disposed in the columns 22-30 and function to suspend theindividual circuit assemblies 10 and heat sink assembly 184 in a stackas illustrated in FIG. 14 so that the plane defined by the surfaces ofthe deformable spacers facing away from the lid 20 is the point ofcontact with adjacent circuit assemblies 10 and heat sink assembly 184or he clamp holding the circuit assemblies in a stack of compressionbonded circuit assemblies 10. As will be described in detail below withregard to FIGS. 5-7, each of the spacers may be either a deformable shimor a deformable spring. The deformable spacers 124-132 are each deformed(within the columns 22-30) by a process described below with referenceto FIG. 13 to provide the circuit assembly 10 with a uniform thicknessmeasured between the surfaces 134-142 of the deformable spacers 124-132and the outside surface of the flat surface 14 within the columns 22-30and further with a uniform thickness measured between the aforementionedsurfaces of the spacers and an outside surface of a heat sink(illustrated in FIG. 13) within the columns 22-30. Load washers 144-152are respectively disposed above deformable spacers 124-132 withincolumns 22-30 for distributing clamping force applied to a stack of atleast one circuit assembly 10 as described with reference to FIG. 14.When the deformable spacers 124-132 have been deformed in accordancewith the process described below with reference to FIG. 13, the topsurfaces 134-142 are disposed within a single plane which is parallel tothe flat regions within the flat surface 14, the flat regions within thelid 20 and the opposed surfaces of the heat sink as described below withreference to FIG. 13. The load washers 144-152 function to uniformlydistribute clamping force to the deformable spacers 134-140 which istransferred through the columns 22-30 to the individual circuit elementsto be compression bonded. An insulating sheet 153 is provided on top ofthe load washers 144-152 to electrically isolate the individual circuitassemblies 10 when they are configured in a stack of circuit assembliesas discussed below with reference to FIG. 14 and retains deformablespacers 124-132 and load washers 144-152 to assembly 10 by adhesive tolid 20.

FIG. 4 illustrates an electrical schematic of the circuit illustrated inFIGS. 1 and 2. As stated above, it should be understood that the presentinvention is not limited to the particular circuit disclosed herein andis applicable to circuits requiring one or more compression bondedcircuit elements which are to be hermetically sealed and stacked in astack of multiple circuits. Moreover, while the control circuit 82,which is delineated by the dotted lines, is illustrated as a Bakerclamp, it should be understood that other control circuitry may bedisposed therein which in the present embodiment is external to thecircuit assembly 10. The circuit of FIGS. 1-4 may be used in an inverterfor generating AC Power in an airframe. Furthermore, the electricalconnections in the interior of the chamber which have been omitted fromFIG. 3 may be determined from FIG. 4. The precise layout of theelectrical connections which have been omitted from FIG. 3 is notcritical and required connections should not be short circuited togetherwithin the hermetically sealed chamber.

FIG. 5 illustrates a deformable spacer 154 which is comprised of anannular section of molded resin which may be deformed by the uniformapplication of force vectors 156 to opposed faces 158. The force vectors156 are the force applied by the process described below with referenceto FIG. 13 by a press of conventional design. The width of the moldedresin 154, as measured across the opposed faces 158, is compressedinelastically from dimension "a" to dimension "b" upon the applicationof compressive force above the elastic limit of the molded resin asdescribed below in FIG. 13 with reference to the manufacturing processof deforming the deformable spacers 124-132 of the present invention.The annulus 160 functions to center the spacer 154 on the axis of thecircular corrugations 114-122 and in columns 22-30. Each corrugation, asillustrated in FIG. 2, has a center raised portion which engages theopening to the annulus on the side facing the lid 20. The moldablematerial may be in accordance with AMS 3726-1-2-3. Alternatively,nondeformable members can be machined while under compressive load toresult in the uniform thickness referred to above.

FIG. 6 illustrates a sectional view of a deformable spring set 162 whichis usable as the deformable spacers 124-132. The deformable spring set162 has a characteristic which permits it to be inelastically deformedwhile retaining a spring rate for maintaining the pressure applied toindividual circuit elements to be compression bonded within the columns22-30 within the range of pressure to be applied during operation as aconsequence of dimensional expansion caused by thermal cycling. Thedeformable spring set 162 is comprised of one or more annular rings madefrom a conventional "C"-seal which rings are concentric to the axes ofthe columns 22-30 when positioned as in FIG. 3. The deformable spring162, as illustrated, has three concentrically disposed rings 164-168.Alternatively, although not illustrated, the deformable spring set 162may have the concentric rings joined together by a connector such asmetal layers joined diametrically to the top and bottom parts of theindividual concentric rings 164-168. The application of force vectors156 to flat rigid surfaces 170 and 172 of a conventional press (notillustrated) inelastically compresses the cross section of the rings164-168 past their yield point to reduce the dimension "a" to adimension, such as "b", between the ends 174 and 176 of the concentricrings 164-168. The compression of the cross section of the concentricrings 164-168 is further described below regarding FIG. 13 with respectto the manufacturing process. The thickness, diameter of the "C", andnumber of concentric rings may be chosen to obtain the desired springrate during thermal cycling within the operating pressure range of thecompression bonded circuit element above which the spring is disposed.

FIG. 7 illustrates a perspective view of a deformable spring 178 madefrom conventional lattice having axial columns extending between faces158 including a plurality of cells 179 in an array. The axial columnsintersect the recesses within the flat section 14 and the lid 20 with anangle which is preferably 90°. The number of cells 179 per unit area andgeometric shape may be varied to obtain a desired spring rate tomaintain pressure within a range of pressure required for particularcircuit elements to be compression bonded. The lattice has the propertyof being inelastically deformable to reduce its dimension, in adirection parallel to the direction of the applied force, from "a" to"b" as is described with reference to FIG. 13 below regarding themanufacturing process while providing a spring rate which appliespressure during thermal cycling within the operating pressure range ofthe compression bonded circuit element above which the lattice isdisposed.

The choice of utilization of the different types of deformable spacers154, 162 and 178 is as follows. When the heat sink, which is describedbelow with reference to FIG. 13, is effective in minimizing thermalexpansion during operation, the molded resin 154 may be utilized whichdoes not have a spring rate chosen to maintain the pressure on thecompression bonded circuit elements within an operating pressurespecified by the circuit elements. When the amount of thermal expansionis minimized by effective heat sinking, the dimensional change of thethickness of the individual deformable spacers 124-132 is so small thatthe pressure applied to the individual circuit elements within thecolumns 22-30 does not fall outside of the specified pressure range foroperation which eliminates the requirement of having a desired springconstant. Alternatively, when the heat sink is not effective in reducingexpansion caused by thermal cycling to a degree to maintain the desiredpressure during operation without compensation for dimensional change,it is necessary to provide deformable springs or a distributed springfunction in the columns 22-30 which will maintain pressure on thecompression bonded individual circuit elements within the columns withinthe specified compressive force of the particular circuit elements. Thespring constant of the individual deformable springs is chosen tomaintain the pressure on the circuit element within its column 22-30within the pressure range specified for the circuit element. It shouldfurthermore be understood that the foregoing examples of materials whichmay be utilized for the deformable springs are not limitations of thepracticing of the invention. It should be understood that othermaterials exhibiting a spring function are usable in the practicing ofthe invention which are inelastically deformable in a direction parallelto the direction of an applied force in accordance with the processdescribe below with reference to FIG. 13 and further which exhibit aspring rate which will maintain pressure on compression bonded circuitelements within the columns 22-30 within the specified operatingpressure range of the circuit elements during thermal cycling.

While in applications requiring a spring rate to compensate for thermalexpansion during operation it is preferred to have the spring functionproduced by the deformable spacers 124-132, it should be understoodalternatively that the spring function may be distributed within thecolumns 22-30 within one or more other elements which may be disposedwithin the hermetically sealed chamber or outside of the chamber. Forexample, the heat sink described below may alternatively contribute partor all of the described spring function. A spring rate in the heat sinkmay be produced as a consequence of the choice of material from whichthe heat sink is made and/or as a consequence of its geometry such as,but not limited to, providing spaced heat radiating structures whichextend parallel to the axes of the columns 22-30.

FIG. 8 illustrates a top plan view of a hermetically sealed circuitassembly 10 in accordance with the invention with the insulative layer153 removed. FIGS. 9-12 illustrate sectional views of FIG. 8.Furthermore, while in FIGS. 9-12 the deformable spacers 124-132 are theC springs illustrated in FIG. 6, it should be understood that thedeformable spacers 124-132 may be either the deformable shims or thedeformable springs of FIGS. 5-7 or other materials having theabove-described properties depending upon the application of the presentinvention as described above.

With reference to FIGS. 9 and 10, the chamber 200 has rounded corners202 and 204 which are provided for strain relief caused by heat buildupby welding or brazing of the lid 20 to the flat section 14. A multiplepin ceramic feedthrough 206 with pins 84 permits wiring connectionsbetween the control circuit 82 within the hermetically sealed chamber200 and the exterior by wires 208 which extend through connector 210.Potting 212, which may be any suitable resin which is thermally stablefor the service conditions, is provided to protect and hold theconnectors 42 and 210. A hermetically sealed feedthrough 214 permitsconnection of the emitter bus 54 to the exterior of the chamber byconnection to the feed through bus 216 of the bus connector 46, ceramicannulus 218 has metal connectors 220 which are joined to the flatsection 14 and connectors 222 which are joined to the base 224 of thefeedthrough 214. Potting 226, which may be any suitable resin which isthermally stable for the service condition, is provided to protect andhold the bus connector 46. Similarly, the feed through 214 connectsdiode bus 52 to bus connector 48 and diode bus 50 to bus connector 44.

The process for deforming the deformable spacers 124-132 in accordancewith the present invention is described with reference to FIG. 13. Aswas described above with reference to FIG. 3, the top surfaces 134-142of the deformable spacers 124-132 are inelastically deformed to bedisposed within a single plane which is parallel to the flat portions offlat surface 14, the flat portions of lid 20 and opposed surfaces 186and 188 of heat sink 184. Deformation of the deformable spacers 124-132is produced by the combination of a spacer deforming press 180 which hasa flat surface 182 which is moved orthogonal with respect to the flatportions of the assembled parallel flat surface 14 and lid 16. Theorthogonal movement of the spacer deforming press 180, which isindicated by the bidirectional arrow 193, may be accomplished by anysuitable mechanical translating mechanism which per se is not part ofthe present invention. In the preferred form of the invention, althoughnot limited thereto, the heat sink 184 is attached to an outside surfaceof the flat surface 14 to form a thermal contact of high conductivity topermit heat generated by the compression bonded semiconductor elementsin each of the circuit assemblies 10 to be effectively conducted to anddissipated by the heat sink. Furthermore, the heat sink may includesuitable manifolds to receive cooling fluids or heat radiating finstructure (not illustrated) to increase the heat conducting propertiesof the heat sink 184 and provide the aforementioned springcharacteristic.

The inside surface 186 and outside surface 188 of the heat sink 184 areparallel to the flat portions of the assembled flat surface 14 and lid20, surface 194 of the support stand 192, and surface 182 of the spacerdeforming press 180. Accordingly, lowering of the spacer deforming press180 by the translating mechanism, as indicated by arrow 193, deforms thedeformable spacers 124-132 so that the thickness of the circuit assemblyin each of the columns 22-30 measured between the surfaces 134-142,within the columns 22-30 and the outside surface of the flat surface 14or the surface 188 of the heat sink 184 is uniform and substantiallyidentical. It is the objective of the process of deforming the spacers124-132 to make the thickness of the columns measured across the outsideof each circuit assembly 10 to be as close as is possible to beingidentical within the constraints of economically manufacturing thecircuit assemblies.

Each of the deformable spacers 124-132 is deformed by the processdescribed above with reference to FIG. 13 to a thickness whichcompensates for variation in thickness of like parts disposed in thecolumns 22-30, for variation in the number and thickness of circuitbuses within the columns such as, for example, with reference to FIG. 2wherein columns 22-26 each contain two circuit buses and columns 28 and30 contain one circuit bus and for variation in the total number ofelements in columns 24-30 as indicated below in Table I.

                  TABLE I                                                         ______________________________________                                                  Column                                                                       22     24     26       28  30                                        ______________________________________                                        Identification                                                                           54       54     54     68  52                                      of part by                            80                                      reference  76       94     76     74  98                                      number     90       78     90     90  100                                                --       92     --     --  102                                                         105                                                       Total number                                                                             3        5      3      3   5                                       of parts                                                                      ______________________________________                                    

By deforming the deformable spacers 124-132 to a thickness to produce auniform thickness measured across each of the columns 22-30 of thecircuit assembly 10, the individual circuit assemblies are easilyclamped into a stack containing multiple circuits which may be uniformlycompression bonded throughout all of the columns 22-30 merely byapplying clamping pressure without having pressure variations outsidethe pressure range specified for the operation of the compression bondedcircuit elements. It should further be understood that the process fordeforming the deformable spacers 124-132 may be implemented with anysuitable pressing apparatus which has the capability of deforming thetop surfaces 134-142 of the deformable spacers 124-132 into a singleplane which is parallel to the flat portions of the assembled flatsurface 14 and lid 20 and surfaces 186 and 188 of the heat sink 184.Furthermore, as described above with reference to FIG. 1, insulativespacers 107 not performing any circuit function may be disposed withinany of the columns 22-30 inside of any of the PG,40 hermetically sealedchambers 200 of the circuit assemblies 10 within a stack of circuitassemblies, as illustrated in FIG. 14, to permit circuit assemblieshaving differing configurations of compression bonded circuit elementsto be compression loaded in a single stack.

FIG. 14 illustrates an exploded view of a stack of a plurality ofindividual circuit assemblies 10 including heat sink assembly 184. Eachof the individual circuit assemblies 10 is preferably, as illustrated inFIG. 13, with a heat sink 184 attached to and in thermal contact withthe outside surface of the flat surface 14. The details of theindividual circuit assemblies 10 have been omitted but it should beunderstood that they are preferably in accordance with FIGS. 1-3 and 13but not limited thereto. Each of the compression bonded circuit elements(not illustrated) of the circuit assemblies 10 are compression bonded bya clamping mechanism 196 having a pair of opposed rigid surfaces 197 and198 which are loaded by a force applied orthogonal thereto. The forcemay be applied by any conventional clamping mechanism (not illustrated)such as a C clamp or other clamps. The individual columns 22-30 of thecircuit assemblies 10 described above are illustrated to identify theorientation of the individual compression bonded circuit elements (notillustrated) in each of the circuit assemblies 10 with respect to thestack of circuit. Because of the raised structure of the deformablespacers when the individual circuit assemblies 10 are assembled as inFIG. 3, the force applied by the surfaces 202 and 204 is equally loadedon each of the columns 22-30 to apply equal compressive force per unitarea to each of the compression bonded circuit elements in each of thecolumns 22-30 within a desired pressure range. The mechanism forapplication of compressive force is conventional and per se does notform part of the present invention.

While the invention has been described in terms of its preferredembodiments, it should be understood that numerous modifications may bemade thereto without departing from the spirit and scope of theinvention as defined in the appended claims. For example, while thepreferred embodiment of the invention has been described with eachhermetically sealed circuit having a heat sink which does not containfins or other heat radiating structures which increase the surface areaof the heat sink or provide cooling fluid in contact with or flowingthrough the heat sink, it should be understood that any structure may beutilized in the heat sink to maximize its heat sinking ability.Furthermore, the invention is not limited to any particular clampingstructure for applying the compressive force to compression bond theindividual circuit elements to be compression bonded when the clamp isapplied to apply compressive force to the columns. Furthermore, whilepreferably the individual circuit assemblies 10 are stacked in a stackof more than one circuit assembly per stack, it should be understoodthat the invention may be practiced with a single hermetically sealedcircuit assembly with compressive force applied thereto. It is intendedthat all such modifications fall within the scope of the appendedclaims.

I claim:
 1. A hermetically sealed circuit assembly containing aplurality of circuit elements which are to be compression bonded uponapplication of a force through opposed first and second walls of ahermetically sealed chamber containing the circuit elements to becompression bonded comprising:a plurality of columns within the chamberwith circuit element to be compression bonded being disposed in aseparate column; an inelastically deformed spring, positioned in each ofthe columns outside the chamber having a first surface facing an outsidesurface of one of the first and second walls of the hermetically sealedchamber and a second surface with each of the second surfaces of thedeformed springs facing an outside surface of another of the first andsecond walls and deformed to compensate for variation in thickness ofparts within the columns; and a thickness of the columns measuredbetween the outside surfaces of the first and second walls prior tocompression bonding being substantially identical.
 2. A hermeticallysealed circuit assembly in accordance with claim 1 wherein:each springhas a spring rate within a range which is a function of the circuitelement to be compression bonded in the column which contains thedeformed spring.
 3. A hermetically sealed circuit assembly in accordancewith claim 2 wherein:each of the second surfaces of the deformed springsare disposed in a single plane.
 4. A hermetically sealed circuitassembly in accordance with claim 3 wherein each spring comprises:atleast one ring with each ring being concentric with an axis of thecolumn within which the ring is contained and having a C-shaped crosssection in which opposite ends of the C are inelastically deformedtoward each other.
 5. A hermetically sealed circuit assembly inaccordance with claim 3 wherein the spring comprises:a lattice havingopen cells defining columns intersecting one of the walls.
 6. Ahermetically sealed circuit assembly in accordance with claim 3 furthercomprising:at least one circuit bus having first and second opposedsurfaces which are substantially parallel to each other and to the firstand second walls of the hermetically sealed circuit assembly, the atleast one circuit bus having at least one corrugation therein.
 7. Ahermetically sealed circuit assembly in accordance with claim 6wherein:the circuit assembly has an opening through which at least onecircuit connection extends, at least one corrugation being within eachof the at least one circuit buses between a circuit connection and apoint of electrical contact with an adjacent circuit element to becompression bonded and at least one corrugation being within each of theat least one circuit buses between adjacent circuit elements to becompression bonded which are in electrical contact with one of the atleast one circuit buses.
 8. A hermetically sealed circuit assembly inaccordance with claim 7 further comprising:a control circuit disposedinside the chamber having circuit control elements for controlling theplurality of circuit elements to be compression bonded within thechamber; and the control circuit has a plurality of contacts which areeach respectively connected to a circuit bus.
 9. A hermetically sealedcircuit assembly in accordance with claim 8 wherein:at least two circuitbuses are contained in the chamber; and portions of one circuit busoverlie another circuit bus within the chamber.
 10. A hermeticallysealed circuit assembly in accordance with claim 1 further comprising:aplurality of circular corrugations within the first wall of the chamberin a spatial configuration with each corrugation determining a spatiallocation within the circuit assembly of a circuit element to becompression bonded; a plurality of circular corrugations within thesecond wall of the chamber in a spatial configuration identical to thespatial configuration of the corrugations in the first wall,corrugations of the second wall respectively being opposed tocorrugations in the first wall with pairs of opposed corrugations in thefirst and second walls defining a column; and a deformed spring beingpositioned outside the chamber within each different corrugation withinthe second wall.
 11. A hermetically sealed circuit assembly inaccordance with claim 10 wherein:the plurality of circular corrugationswithin the first wall each form a recess which projects outward from thechamber; the plurality of circular corrugations within the second walleach form a recess which projects inward toward the chamber; and each ofthe deformed springs is positioned within a different one of therecesses within the second wall and a single plane being spaced from thesecond wall of the chamber to an exterior side of the chamber.
 12. Ahermetically sealed circuit assembly in accordance with claim 1 furthercomprising:a heat sink having first and second parallel surfaces withthe first surface of the heat sink being in surface and thermal contactwith an outside surface of the first wall.
 13. A hermetically sealedcircuit assembly in accordance with claim 1 wherein:each column of thehermetically sealed circuit assembly contains a circuit element to becompression bonded.
 14. A hermetically sealed circuit assemblycontaining a plurality of circuit elements which are to be compressionbonded upon application of a force respectively through opposed firstand second walls of a hermetically sealed chamber containing the circuitelements to be compression bonded comprising:a plurality of columnswithin the chamber with each circuit element to be compression bondedbeing disposed in a separate column; an inelastically deformed spacer,positioned in each of the columns outside the chamber having a firstsurface facing an outside surface of one of the first and second wallsof the hermetically sealed chamber and a second surface with each of thesecond surfaces of the deformed spacers facing an outside surface ofanother of the fist and second walls and deformed to compensate forvariation in thickness of parts within the columns; and a thickness ofthe columns measured between the outside surfaces of the first andsecond walls prior to compression bonding being substantially identical.15. A hermetically sealed circuit assembly in accordance with claim 14wherein:each of the second surfaces of the deformed springs are disposedin a single plane.
 16. A hermetically circuit assembly in accordancewith claim 15 further comprising:at least one circuit bus having firstand second opposed surfaces which are substantially parallel to eachother and to the first and second walls of the hermetically sealedcircuit assembly, the at least one circuit bus having at least onecorrugation therein.
 17. A hermetically sealed circuit assembly inaccordance with claim 16 wherein:the circuit assembly has an openingthrough which at least one circuit connection extends, at least onecorrugation being within each of the at least one circuit buses betweenthe circuit connection and a point of electrical contact with a circuitelement to be compression bonded and at least one corrugation beingwithin each of the at least one circuit buses between circuit elementsto be compression bonded which are in electrical contact with one of theat least one circuit buses.
 18. A hermetically sealed circuit assemblyin accordance with claim 17 further comprising:a control circuitdisposed inside the chamber having circuit control elements forcontrolling the plurality of circuit elements to be compression bondedwithin the chamber; and the control circuit having a plurality ofcontacts which are each respectively connected to a different buses. 19.A hermetically sealed circuit assembly in accordance with claim 18wherein:at least two circuit buses are contained in the chamber; andportions of one circuit bus overlie another circuit bus within thechamber.
 20. A hermetically sealed circuit assembly in accordance withclaim 14 further comprising:a plurality of circular corrugations withinthe first wall of the chamber in a spatial configuration with eachcorrugation determining a spatial location within the circuit assemblyof a circuit element to be compression bonded; a plurality of circularcorrugations within the second wall of the chamber in a spatialconfiguration identical to the spatial configuration of the corrugationsin the first wall, corrugations of the second wall respectively beingopposed to corrugations in the first wall with pairs of opposedcorrugations in the first and second walls defining a column; and adeformed spacer being positioned outside the chamber within acorrugation within the second wall.
 21. A hermetically sealed circuitassembly in accordance with claim 20 wherein:the plurality of circularcorrugations within the first wall each form a recess which projectsoutward from the chamber; the plurality of circular corrugations withinthe second wall each form a recess which projects inward toward thechamber; and each of the different deformed spacers is positioned withina different one of the recesses within the second wall and a singleplane being spaced from the second wall of the chamber to an exteriorside of the chamber.
 22. A hermetically sealed circuit assembly inaccordance with claim 14 further comprising:a heat sink having first andsecond parallel surfaces with the first surface of the heat sink beingin surface and thermal contact with an outside surface of the firstwall.
 23. A hermetically sealed circuit assembly in accordance withclaim 14 wherein:the spacers are springs.
 24. A hermetically sealedcircuit assembly in accordance with claim 14 wherein:the spacers areshims.
 25. A hermetically sealed circuit assembly in accordance withclaim 14 wherein:each column of the hermetically sealed circuit assemblycontains a circuit element to be compression bonded.
 26. A hermeticallysealed circuit assembly containing a plurality of circuit elements whichare to be compression bonded upon application of a force respectivelythrough opposed first and second walls of a hermetically sealed chambercontaining the circuit elements to be compression bonded comprising:aplurality of columns within the chamber with each circuit element to becompression bonded being disposed in a separate column; an inelasticallydeformed shim, positioned in each of the columns outside the chamberhaving a first surface facing an outside surface of one of the first andsecond walls of the hermetically sealed chamber and a second surfacewith each of the second surfaces of the deformed shims facing an outsidesurface of another of the first and second walls and deformed tocompensate for variation in thickness of parts within the columns; and athickness of the columns measured between the outside of the first andsecond walls prior to compression bonding being substantially identical.27. A hermetically sealed circuit assembly in accordance with claim 26wherein:each of the second surfaces of the deformed springs are disposedin a single plane.
 28. A hermetically sealed circuit assembly inaccordance with claim 26 further comprising:a plurality of circularcorrugations within the first wall of the chamber in a spatialconfiguration with each corrugation determining a spatial locationwithin the circuit of a circuit element to be compression bonded; aplurality of circular corrugations within the second wall of the chamberin a spatial configuration identical to the spatial configuration of thecorrugations in the first wall, corrugations of the second wall beingrespectively opposed to corrugations in the first wall with pairs of theopposed corrugations in the first and second walls defining a column;and a deformed shim being positioned within a corrugation within thesecond wall.
 29. A hermetically sealed circuit assembly in accordancewith claim 28 wherein:the plurality of circular corrugations within thefirst wall each form a recess which projects outward from the chamber;the plurality of circular corrugations within the second wall each forma recess which projects inward toward the chamber; and each of thedifferent deformed shims is positioned within a different one of therecesses within the second wall and a single plane being spaced from thesecond wall of the chamber to an exterior side of the chamber.
 30. Ahermetically sealed circuit assembly in accordance with claim 26 furthercomprising:at least one circuit bus having first and second opposedsurfaces which are substantially parallel to each other and to the firstand second walls of the hermetically sealed circuit assembly, the atleast one circuit bus having at least one corrugation therein.
 31. Ahermetically sealed circuit assembly in accordance with claim 30wherein:the circuit assembly has an opening through which at least onecircuit connection extends, at least one corrugation being within eachat least one circuit bus between the circuit connection and a point ofelectrical contact with a circuit element to be compression bonded andat least one corrugation being within each of the at least one circuitbuses between circuit elements to be compression bonded which are inelectrical contact with one of the at least one circuit buses.
 32. Ahermetically sealed circuit assembly in accordance with claim 31 furthercomprising:a control circuit disposed inside the chamber having circuitcontrol elements for controlling the plurality of circuit elements to becompression bonded within the chamber; and the control circuit having aplurality of contacts which are each respectively connected to adifferent buses.
 33. A hermetically sealed circuit assembly inaccordance with claim 32 wherein:at least two circuit buses arecontained in the chamber; and portions of one circuit bus overlieanother circuit bus within the chamber.
 34. A hermetically sealedcircuit assembly in accordance with claim 26 further comprising:a heatsink having first and second parallel surfaces with the first surface ofthe heat sink being in surface and thermal contact with an outsidesurface of the first wall.
 35. A hermetically sealed circuit assembly inaccordance with claim 26 wherein:each column of the hermetically sealedcircuit assembly contains a circuit element to be compression bonded.36. A hermetically sealed circuit assembly containing at least onecircuit element which is to be compression bonded upon application of aforce through opposed first and second walls of a hermetically sealedchamber containing the circuit elements to be compression bondedcomprising:a plurality of columns within the chamber with each circuitelement to be compression bonded being disposed in a separate column, aspacer being disposed in at least one column inside the hermeticallysealed chamber and each column having a spacer not performing a circuitfunction; an elastically deformed spring, positioned in each of thecolumns outside the chamber having a first surface facing an outsidesurface of one of the first and second walls of the hermetically sealedchamber and a second surface with each of the second surfaces of thedeformed springs facing an outside surface of the first and second wallsand deformed to compensate for variation in thickness of parts withinthe columns; and a thickness of the columns measured between the outsidesurfaces of the first and second walls prior to compression bondingbeing substantially identical.
 37. A hermetically sealed circuitassembly containing a plurality of circuit elements which are to becompression bonded upon application of a force through opposed first andsecond walls of a hermetically sealed chamber containing the circuitelements to be compression bonded comprising:a plurality of columnswithin the chamber with each circuit element to be compression bondedbeing disposed in a separate column; an inelastically deformed spacer,positioned in each of the columns outside the chamber having a firstsurface facing an outside surface of one of the first and second wallsof the hermetically sealed chamber and a second surface with each of thesecond surfaces of the deformed spacers facing an outside surface ofanother of the first and second walls and deformed to compensate forvariation in thickness of parts within the columns; a thickness of thecolumns measured between the outside surfaces of the first and secondwalls prior to compression bonding being substantially identical; and adistributed spring function contained in at least one element withineach column.
 38. A hermetically sealed circuit assembly in accordancewith claim 37 wherein:the spring function has a spring rate within arange which is a function of the circuit element to be compressionbonded in the column which contains the distributed spring function. 39.A hermetically sealed circuit assembly in accordance with claim 38wherein:the at least one element is the deformed spacer and a heat sinkhaving opposed parallel surfaces with one of the opposed parallelsurfaces facing one of the walls.
 40. A circuit assembly containing aplurality of circuit elements which are to be compression bonded uponapplication of a force through opposed first and second walls containingthe circuit elements to be compression bonded comprising:a plurality ofcolumns between the walls with each circuit element to be compressionbonded being disposed in a separate column; an inelastically deformedelement, positioned in each of the columns having a first surface facingan outside surface of one of the first and second walls and a secondsurface with each of the second surfaces of the deformed elements facingan outside surface of another of the first and second walls and deformedto compensate for variation in thickness of parts within the columns;and a thickness of the columns measured between the outside surfaces ofthe first and second walls prior to compression bonding beingsubstantially identical.
 41. A circuit assembly in accordance with claim40 wherein:each element has a spring rate within a range which is afunction of the circuit element to be compression bonded in the columnwhich contains the deformed element.
 42. A circuit assembly inaccordance with claim 40 wherein:each of the second surfaces of thedeformed elements are disposed in a single plane.